Polysulfone nanocomposite optical plastic article and method of making same

ABSTRACT

An optical nanocomposite material has a nanoparticulate filler dispersed in a host plastic material. According to the method of making the nanocomposite material, a predetermined temperature sensitive optical vector, such as refractive index, of the plastic host material and nanoparticulate filler are directionally opposed resulting in a nanocomposite material having significantly improved stability of the refractive index with respect to temperature.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application is related to U.S. application Ser. No.(D-82044), filed Dec. 22, 2000, by Border, et al., and entitled,“Polymethylmethacrylate Nanocomposite Optical Plastic Article And MethodOf Making Same;” U.S. application Ser. No. (D-82045), filed Dec. 22,2000, by Border, et al., and entitled, “Cyclic Olefin PolymericNanocomposite Optical Plastic Article And Method Of Making Same;” U.S.application Ser. No. (D-82046), filed Dec. 22, 2000, by Border, et al.,and entitled, “Polystyrene Nanocomposite Optical Plastic Article AndMethod Of Making Same;” U.S. application Ser. No. (D-82047), filed Dec.22, 2000, by Border, et al., and entitled, “Polycarbonate NanocompositeOptical Plastic Article And Method Of Making Same;” U.S. applicationSer. No. (D-8 1169), filed Dec. 22, 2000, by Border, et al., andentitled, “Reduced Temperature Sensitive Polymeric Optical Article AndMethod Of Making Same.”

FIELD OF THE INVENTION

[0002] The invention relates generally to the field of polymeric opticalarticles. More particularly, the invention concerns polymeric opticalmaterials and articles, such as plastic lenses, that maintain stableperformance characteristics over a broad temperature range.

BACKGROUND OF THE INVENTION

[0003] Plastic lenses and glass lenses often perform the same functionin optical systems, such as in cameras, microscopes, telescopes andopthalmic wear. The two main attributes that separate plastic lensesfrom glass lenses are cost and optical stability. Plastic lensestypically cost 1/100^(th) the price of a similar glass lens. On theother hand, the stability of the refractive index of a glass lens withrespect to temperature and humidity is typically 100 times better thanthat of a plastic lens.

[0004] The difference in cost is due largely to the difference inmanufacturing processes that are required for the two materials and therelative temperatures that the materials must be formed at. Plasticlenses are typically produced at 230° C. using injection molding atcycle times that are 10 times faster than glass lenses that are largelyproduced by grinding and polishing or compression molding at 625° C.Grinding and polishing are labor intensive while the high temperaturesthat glass must be formed at requires expensive mold materials andextensive maintenance costs.

[0005] In contrast, the difference in optical stability between plasticand glass is due to differences in their basic material properties. Thisdifference in optical stability results in substantially more variationin focus and image quality in articles such as cameras when plasticlenses are used in place of glass. What is desired, and a remainingchallenge in the art, is a material with the optical stability of glassthat processes like a plastic. While optical plastic materials such ascyclic olefins greatly improve the refractive index stability withrespect to humidity, improving the refractive index stability withrespect to temperature has remained an opportunity. A study on thecompeting fundamental material characteristics that determine the signand the magnitude of the dn/dT of glasses is available, for instance, byLucien Prod'homme, “A new approach to the thermal change in therefractive index of glasses,” Physics and Chemistry of Glasses, Vol. 1,No. 4, Aug. The two competing effects that determine the dn/dT inglasses are the density change which produces a negative dn/dT and theelectronic polarizability which produces a positive dn/dT. The net dn/dTin a glass material depends on which effect dominates. In opticalplastics however, there is not an electronic polarizability so that allunfilled materials have negative dn/dT values. None the less, thearticle by Prod'homme does identify the possibility of using glass-likefillers with positive dn/dT values to substantially alter the dn/dT of afilled plastic composite material.

[0006] Nanoparticulate fillers have been used to modify the index ofrefraction of optical plastics. By using a filler small enough that itis well below the wavelength of visible light (400-700 nm), the fillerwill not scatter the light and the filled plastic can retain itstransparency. WIPO Patent W097/10527 describes the use of nanoparticlesto increase the refractive index of plastics for opthalmic applications.In addition, technical references that describe the addition ofnanoparticles to increase the refractive index of plastics include: C.Becker, P Mueller, H. Schmidt; “Optical and ThermomechanicalInvestigations on Thermoplastic Nanocomposites with Surface-ModifiedSilica Nanoparticles,” SPIE Proceedings Vol. 3469, pp. 88-98, July 1998;and, B. Braune, P. Mueller, H. Schmidt; “Tantalum Oxide Nanomers forOptical Applications,” SPIE Proceedings Vol 3469, pp. 124-132, July1998. While these references disclose the use of nanoparticles to modifyrefractive index of optical plastics they do not discuss the issue ofrefractive index stability with respect to temperature which requires adifferent set of characteristics in the nanoparticle.

[0007] U.S. Pat. No. 6,020,419 issued to M. Bock, et al., discloses theuse of nanoparticulate fillers in a resin based coating for improvedscratch resistance. U.S. Pat. No. 5,726,247 issued to M. Michalczyk, etal., also describes a protective coating that incorporates inorganicnanoparticles into a fluoropolymer. While scratch resistance isimportant in plastic optics, the nanoparticles that would be suitablefor scratch resistance would be very different from those with thespecific properties needed to improve refractive index stability withrespect to temperature.

[0008] U.S. Pat. No. 3,915,924 issued to J. H. Wright describes ananoparticulate filled clear material for filling voids. U.S. Pat. No.5,910,522 issued to H. Schmidt, et al., describes an adhesive foroptical elements that includes nanoscale inorganic particles to reducethermal expansion and improved structural properties at elevatedtemperatures. While the inventions described in these patents representssome progress in the art, none of them address specific opticalproperties of the modified plastic material particularly as theseproperties relate to temperature sensitivity.

[0009] WIPO Patent WO9961383al discloses a method for producingmultilayered optical systems that uses at least one layer that containsnanoparticulate fillers to form a layer with a different refractiveindex than the substrate to create an interference filter or anantireflection layer. Obviously, this patent is addressing another formof modification of the index of refraction and such is not concernedwith the stability of the index of refraction with respect totemperature.

[0010] Skilled artisans will appreciate that a wide variety of materialsare available in nanometer particle sizes that are well below thewavelength of visible light. Representative materials may be acquiredfrom companies such as Nanophase Technologies Corporation andNanomaterials Research Corporation. By selecting nanoparticle materialsbased on properties other than index of refraction, our experienceindicates that it is now possible to modify other optical properties ofplastics.

[0011] While there have been several attempts to modify properties ofplastics using nanoparticles, none of these attempts have provensuccessful in producing optical plastic articles with temperature stableoptical properties while retaining important processing characteristics.

[0012] Therefore, a need persists in the art for optical plasticarticles, such as lenses, and a method of making same that havetemperature stable optical properties.

SUMMARY OF THE INVENTION

[0013] It is, therefore, an object of the invention to provide anoptical nanocomposite material that has reduced temperature sensitivity.

[0014] Another object of the invention is to provide an optical article,such as a plastic lens, that maintains stability over a broad range oftemperatures.

[0015] Yet another object of the invention is to provide a method ofmanufacturing an optical article having reduced temperature sensitivity.

[0016] It is a feature of the optical article of the invention that aselect nanoparticulate dispersed into a plastic host material having atemperature sensitive optical vector that is directionally opposed tothe temperature sensitive optical vector of the nanoparticulate filler.

[0017] To accomplish these and other objects, features and advantages ofthe invention, there is provided, in one aspect of the invention, apolysulfone nanocomposite optical plastic article comprising: apolysulfone host material having a temperature sensitive optical vectorx₁ and nanoparticles dispersed in said polysulfone host material havinga temperature sensitive optical vector x₂, wherein temperature sensitiveoptical vector x₁ is directionally opposed to temperature sensitiveoptical vector x₂

[0018] In another aspect of the invention, there is provided a method ofmanufacturing a polysulfone nanocomposite optical plastic article,comprising the steps of:

[0019] (a) providing a polysulfone host material having a temperaturesensitive optical vector x₁ and nanoparticles having a temperaturesensitive optical vector X_(2,), wherein temperature sensitive opticalvector x₁ is directionally opposed to temperature sensitive opticalvector x₂;

[0020] (b) dispersing said nanoparticles into said polysulfone hostmaterial forming a polysulfone nanocomposite material; and,

[0021] (c) forming said nanocomposite material into said polysulfonenanocomposite optical plastic article.

[0022] Hence, the present invention has numerous advantageous effectsover existing developments, including: (1) the resulting nanocompositehas a significantly lower dn/dT (change in refractive index withtemperature); (2) lenses made with the nanocomposite material have morestable focal length over a given temperature range; (3) low levels ofdn/dT are achievable in the nanocomposite material with reduced loadingof the nanoparticulate; (4) the viscosity of the nanocomposite materialis not significantly higher than the base plastic so that conventionalplastic processing techniques can be used; and, (5) the nanocompositematerial has improved barrier properties so that the change ofrefractive index with respect to humidity will be reduced compared tothe base plastic.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The above and other objects, features, and advantages of thepresent invention will become more apparent when taken in conjunctionwith the following description and drawings wherein identical referencenumerals have been used, where possible, to designate identical featuresthat are common to the figures, and wherein:

[0024]FIG. 1 is a plastic lens showing a range of focal length variationproduced by a change in temperature and the resulting change inrefractive index;

[0025]FIG. 2a shows a lens made from a nanocomposite material that hasimproved stability of refractive index with respect to temperature andan associated reduced range of focal length variation produced by achange in temperature;

[0026]FIG. 2b shows a representative view of the nanocomposite materialbefore forming into an optical article;

[0027]FIG. 3 is a block diagram of the process for manufacturing aplastic optical article with improved refractive index stability;

[0028]FIG. 4 is a schematic diagram of a nanocomposite material makingprocess based on compounding; and,

[0029]FIG. 5 is a schematic diagram of a nanocomposite material makingprocess based on solvent dispersion.

DETAILED DESCRIPTION OF THE INVENTION

[0030] Referring first to FIG. 1, it is well known that in a typicalprior art lens 1, focal length varies significantly with changes intemperature (T). The relationship between focal length and refractiveindex is given by the below equation:

f=R/(n−1);   Equation (1)

[0031] wherein (f) is the focal length of the lens 1 produced asincident light 3 goes through the lens 1 and is focused at focal point5, (R) is the radius of the lens surface, and (n) is the refractiveindex of the lens material. In the case of a camera lens (not shown),the temperature range of operation can easily be 50° C. when used tophotograph a tropical island and then later used to photograph a snowymountain. As an example, a lens 1 having a 10 mm radius and made, forinstance, of polymethylmethacrylate, the index of refraction (n) at roomtemperature is 1.492 and the focal length (calculated from Equation 1above) is 20.325 mm.

[0032] In a typical prior art lens 1 comprising a plastic materialselected from Table I, the change in refractive index (dn) over thetemperature range of operation is 0.0055 and the change in focal point 5shown as the change in focal length 7 (FIG. 1) of the lens from Equation1 is 0.225 or 1%. Skilled artisans will appreciate that the imagequality of images made with the lens 1 will not be the same over theentire operating temperature range due to variations in focus quality.

[0033] Turning now to FIG. 2a, the reduced temperature sensitive,nanocomposite optical article or lens 10 of the invention isillustrated. According to FIG. 2a, the nanocomposite optical article orlens 10 is composed of a plastic host material 16 and a selectnanoparticulate material dispersed in the plastic host material 16.Polymeric host material 16 may be either a thermoplastic or thermosetmaterial. It is important to the invention that the polymeric hostmaterial be selected based on a predetermined temperature sensitiveoptical vector x₁, for instance refractive index n. Similarly, theselection of the nanoparticulate material dispersed in the polymerichost material 16 must be based on a corresponding predeterminedtemperature sensitive optical vector x₂, specifically refractive index.In this case, temperature sensitive optical vectors x₁ and x₂ aredefined by a change in refractive index (dn) of the polymeric hostmaterial 16 and the nanoparticulate material, respectively, with respectto a change in temperature (dT). It is further important to ourinvention that x₁ is directionally opposed to x₂ By carefully selectinga nanoparticulate material having a dn/dT, i.e., a rate of change ofrefractive index with respect to temperature, that has a sign that isdirectionally opposed to the dn/dT of the polymeric host material 16, itis possible to significantly reduce the dn/dT of the resultingnanocomposite material at relatively low loadings of the nanoparticulatematerial. As a result, the viscosity of the nanocomposite material isnot drastically increased and the processing characteristics will besimilar to other optical plastics. Consequently, the resulting opticalnanocomposite lens 10 has a focal length range 12 (FIG. 2a) over theoperating temperature range that is much less than that exhibited by theprior art lens 1 shown in FIG. 1. According to Tables I and II, severalselect dn/dT values for polymeric host materials (plastics) andinorganic nanoparticulate fillers that comprise the nanocompositematerial of the invention are illustrated. TABLE 1 Approximate dn/dT forVarious Optical Plastics Plastic dn/dT (10⁻⁶/° C.)Polymethylmethacrylate −105 Polystyrene −127 Polycarbonate −114Polystyrene −110 Cyclic olefin copolymer −102 Polysulfone −100

[0034] TABLE 2 Approximate dn/dT for Various Inorganic Materials withTransmission Bands in Visible Wavelengths Material dn/dT (10⁻⁶/° C.)Barium fluoride −1 Aluminum oxide 14 ALON 12 Berryllium oxide 1 BBO −1Diamond 10 Calcium carbonate 7 Calcium fluoride −1 Cesium bromide −85Cesium iodide −99 Pottasium bromide −4 Pottasium chloride −3 Pottasiumfluoride −23 Pottasium iodide −45 Pottasium titano phosphate 12 Lithiumborate −7 Lithium fluoride −1 Lithium iodate −8 Magnesium aluminateMagnesium oxide 19 Sodium bromide −4 Sodium chloride −35 Sodium fluoride−13 Sodium iodide −5 Silicon oxide −5 Quartz 12 Telurium oxide 9Titanium dioxide −1 Yttrium oxide 8 Zinc Sulfide 49

[0035] In addition to the polymeric host material 16 and thenanoparticulate material having directionally opposed dn/dT, theinvention contemplates other qualifications for the nanoparticulatematerial to make the useful, novel and unobvious optical nanocompositematerial of the invention. For instance, the nanoparticulate materialmust be transparent in the wavelength region of interest to maintainhigh optical transmission levels. Moreover, the nanoparticulate must beavailable in a particle size range that is less than 40 nm to avoidscattering light. Most preferred is a particle size range below 20 nm.Further, it must be possible to disperse the nanoparticles into the baseor host plastic such that no significant amounts of agglomerates and/orvoids larger than 40 nm occur which would scatter light. FIG. 2b shows arepresentative view 15 of the nanoparticles 14 dispersed into theplastic host material 16. The nanoparticles 14 are shown dispersedevenly throughout the host material 16. The nanoparticles 14 do not haveany larger agglomerates or voids associated with them. Furthermore, thecost of the nanoparticulate and any associated surface treatments of thenanoparticles to improve dispersibility must be low enough that thetotal cost of the optical article is significantly less than a glassarticle.

[0036] As illustrated in Tables I and II, there exists a number ofinorganic materials that have dn/dT values with an opposite signcompared to polymeric host materials. Thus, a nanocomposite materialwith significantly improved refractive index stability with respect totemperature can be formulated by dispersing a select nanoparticulatematerial into a polymeric host material 16 that have directionallyopposed (or opposite signs) dn/dT.

[0037] According to another aspect of the invention, a method ofmanufacturing a reduced temperature sensitive optical article or lens 10(as described above) includes the step of selecting a polymeric hostmaterial 16, such as one described in Table 1. According to theinvention, the selected polymeric host material 16 has a temperaturesensitive optical vector x₁ or dn/dT, as described above. Ananoparticulate material (Table II) is selected for dispersing in theplastic host material 16. The select nanoparticulate material, accordingto the invention, is required to have a compatible correspondingtemperature sensitive optical vector x_(2,). Moreover, it is furtherimportant to the invention that x₁ is directionally opposed to x₂, i.e.,one of the two must be negative and the other positive. Once thenanoparticulate material is selected, it is then dispersed in the hostmaterial 16 using suitable dispersion techniques, such as compounding orsolvent dispersion. Once the nanoparticulate material is dispersed intothe polymeric host material 16, a nanocomposite material is formed. Thenanocomposite material can then be used to form an array of opticalarticles such as the lens 10 of the invention having reduced temperaturesensitivity.

[0038] Referring to FIG. 3, a diagram of the method 20 for making thereduced dn/dT nanocomposite material for optical articles, such as lens10, is depicted. First the polymeric host plastic material 22 isselected based on optical, structural and thermal design considerationssuch as % transmission, % haze, index of refraction, yield strength at atemperature, impact strength, scratch resistance, glass transitiontemperature, etc. Second, the nanoparticulate material 24 is preferablyselected based on dn/dT, transparency in the wavelength region ofinterest, particle size, cost, and availability. As disclosed in thisinvention, selecting suitable nanoparticulate materials 24 requiresselecting materials having a dn/dT that has a sign that is opposite tothe host plastic material being used and an average particle size lessthan about 40 nm. Third, the nanoparticles are preferably dispersed 26into the host material although other mixing processes could be used,such as roll milling. Dispersion 26 can be accomplished throughpreferably compounding (refer to FIG. 4) even though solvent dispersion(refer to FIG. 5) can be used with good results. Fourth, the opticallymodified material 28 is formed into an optical article or lens 10 of theinvention.

[0039] Referring to FIGS. 4 and 5, two methods of dispersing thenanoparticles into the host material are schematically illustrated.According to FIG. 4, an outline of the process for dispersion throughcompounding 32 is depicted. In compounding 32, the selectednanoparticles 36 are fed into a compounder 40, such as a twin screwextruder or a Farrell continuous mixer, along with pellets of theselected host material 34. After compounding 40, the optically modifiedmaterial is pelletized 42 for use in an injection molding machine (notshown). As shown in FIGS. 4 and 5, a surface treatment 38 and 52,respectively, may be needed to make the nanoparticles 36 compatible withthe host material 34. Skilled artisans will appreciate that thistreatment could be applied to the nanoparticles 36 directly or added asan additive to the compounder 40 along with the nanoparticles 36 and thehost material 34.

[0040] According to FIG. 5, in the solvent-based dispersion process 44,the selected host plastic material 46 and the selected nanoparticles 48are dispersed in solvents 50, 54, respectively, prior to mixing 56 thetwo solvent solutions. The selected nanoparticles 48 are preferablyexposed to an intermediate solvent dispersion step 54 to insure that agood dispersion is obtained and all agglomerates are broken up. Aftermixing the two solvent solutions together in step 56, the solvents areremoved in step 58 and the optically modified material is pelletized 60for use in an injection molding machine (not shown).

[0041] Following both techniques for making the optically modifiedmaterial, the end result is plastic pellets which contain fullydispersed nanoparticles such as shown in FIG. 2b with the nanoparticlesbeing present in sufficient quantity to deliver the reduced dn/dTdesired.

[0042] Injection molding, compression molding and casting are the threepreferred techniques for forming the optical article 10 (refer to FIG. 3step 28) of the invention.

[0043] In a preferred embodiment, the nanocomposite optical article ofmanufacture 10 is comprised of a polymeric host material selected fromthe group consisting of thermoplastic materials and thermoset materials.Thermoplastic materials used in optical articles include:polymethylmethacrylate, polycarbonate, polystyrene, polysulfone, cyclicolefins, and blends and copolymers of those listed. Thermoset materialsused in optical articles include: diallyl glycolcarbonate, epoxides, andthermoset polyesters.

[0044] Typically the reduced dn/dT article of manufacture 10 producedwithin the contemplation of the invention are simple lenses, an array oflenses, opthalmic lenses, window glazing, optical fibers, cover glassesfor digital imagers, microlenses on digital imagers, and other opticaldevices of the like.

[0045] Skilled artisans will appreciate that modification of the opticalproperties of the host material is achieved, in accordance with themethod of the invention, by reducing the dn/dT of the nanocompositematerial. In our preferred embodiment, this is achieved by dispersing ananoparticulate material filler having a dn/dT with a sign that isopposite that of the base plastic.

EXAMPLE 1

[0046] An exemplary example of the aforementioned procedure for reducingthe dn/dT of an optical plastic follows.

[0047] Polymethylmethacrylate nanocomposite optical plastic comprises apolymethylmethacrylate host material having a temperature sensitiveoptical vector x₁ and a magnesium oxide nanoparticles having atemperature sensitive optical vector x₂ dispersed in thepolymethylmethacrylate host material. According to the requirements ofthe invention, x₁ is directionally opposed to x₂.

[0048] More particularly, a polymethylmethacrylate host material isoptically modified with the addition of magnesium oxide nanoparticles.Polymethylmethacrylate has a dn/dT of approximately −110E-6/° C. asshown in Table 1. Magnesium oxide has a dn/dT of approximately +19E-6/°C. Magnesium oxide nanoparticles are available from Nano MaterialsResearch in the 10 nm size. Magnesium oxide is transparent in the region0.35-6.8 micron which includes the visible light region. The volume (%)of magnesium oxide nanoparticles required in the polymethylmethacrylatehost material to reduce the dn/dT by 50% can be calculated based onvolume using Equation 2, below.

v ₅₀=0.5(γ_(p)/γ_(p)−γ_(n))   Equation (2)

[0049] Wherein, v₅₀ is the volume % of the nanoparticles needed toreduce the dn/dT of the nanocomposite by 50% compared to the hostplastic; γ_(p) is the dn/dT of the host plastic (See FIG. 1); γ_(n) isthe dn/dT of the nanoparticle material.

[0050] For the combination of polymethylmethacrylate and magnesiumoxide, the volume (%) of nanoparticles needed to reduce the dn/dT of thenanocomposite by 50% compared to the dn/dT of the polymethylmethacrylateis approximately 42%.

[0051] Referring to FIG. 4, magnesium oxide nanoparticles werecompounded into polymethylmethacrylate. In this case, a compatibilizeradditive, Solsperse 21000 from Avecia Ltd. at 10% by weight of thenanoparticles was mixed in with the polymethylmethacrylate pellets toaid in dispersing the magnesium oxide nanoparticles. Compounding wasdone in a twin screw extruder. Lenses were then molded from the pelletsproduced from compounding. The resulting dispersion of the nanoparticlesin the lenses was quite good when examined under the scanning electronmicroscope.

EXAMPLE 2

[0052] Alternatively, the nanocomposite material above was preparedusing a solvent based dispersion process as shown schematically in FIG.5, with toluene or xylene. The solvent based dispersion process has beensuccessful for wide variety of polymers (polymethylmethacrylate,polystyrene, polycarbonate and cyclic olefin) as well as a variety ofnanoparticles (titanium dioxide, magnesium oxide and zinc oxide). Thedispersion of the nanoparticles is accomplished in a mill to break upthe agglomerates. As a result, well-dispersed solutions have beenproduced.

[0053] Referring again to FIG. 5, solvent removal 58 can be accomplishedat moderate temperature with vacuum. The dried material is then runthrough an extruder to form pellets. The pellets are then injectionmolded into optical articles using the process in Example 1.

EXAMPLE 3

[0054] In another case, a polycarbonate host material is opticallymodified with the addition of aluminum oxide nanoparticles.Polycarbonate has a dn/dT of approximately −114E-6/° C. as shown inTable 1. Aluminum oxide has a dn/dT of approximately +14E-6/° C.Aluminum oxide nanoparticles are available from Kemco InternationalAssociates in the 37 nm size. Aluminum oxide is transparent in theregion 0.19-5.0 micron which includes the visible light region. Thevolume (%) of aluminum oxide nanoparticles required in the polycarbonatehost material to reduce the dn/dT by 50% can be calculated based onvolume using Equation 2, below.

v ₅₀=0.5(γ_(p)/γ_(p)−γ_(n))   Equation (2)

[0055] Wherein, v₅₀ is the volume % of the nanoparticles needed toreduce the dn/dT of the nanocomposite by 50% compared to the hostplastic; γ_(p) is the dn/dT of the host plastic (See FIG. 1); γ_(n) isthe dn/dT of the nanoparticle material.

[0056] For the combination of polycarbonate and aluminum oxide, thevolume (%) of nanoparticles needed to reduce the dn/dT of thenanocomposite by 50% compared to the dn/dT of the polycarbonate isapproximately 45%.

EXAMPLE 4

[0057] In another case, a polystyrene host material is opticallymodified with the addition of aluminum oxide nanoparticles. Polystyrenehas a dn/dT of approximately −127E-6/° C. as shown in Table 1. Aluminumoxide has a dn/dT of approximately +14E-6/° C. Aluminum oxidenanoparticles are available from Kemco International Associates in the37 nm size. Aluminum oxide is transparent in the region 0.19-5.0 micronwhich includes the visible light region. The volume (%) of aluminumoxide nanoparticles required in the polycarbonate host material toreduce the dn/dT by 50% can be calculated based on volume using Equation2, below.

v ₅₀=0.5(γ_(p)/γ_(p)−γ_(n))   Equation (2)

[0058] Wherein, v₅₀ is the volume % of the nanoparticles needed toreduce the dn/dT of the nanocomposite by 50% compared to the hostplastic; γ_(p) is the dn/dT of the host plastic (See FIG. 1); γ_(n) isthe dn/dT of the nanoparticle material.

[0059] For the combination of polycarbonate and aluminum oxide, thevolume (%) of nanoparticles needed to reduce the dn/dT of thenanocomposite by 50% compared to the dn/dT of the polycarbonate isapproximately 45%.

EXAMPLE 5

[0060] In another case, a cyclic olefin homopolymer host material isoptically modified with the addition of magnesium oxide nanoparticles.Cyclic olefin homopolymer has a dn/dT of approximately −110E-6/° C. asshown in Table 1. Magnesium oxide has a dn/dT of approximately +14E-6/°C. Magnesium oxide nanoparticles are available from Nano MaterialsResearch in the 10 nm size. Magnesium oxide is transparent in the region0.35-6.8 micron which includes the visible light region. The volume (%)of magnesium oxide nanoparticles required in the cyclic olefinhomopolymer host material to reduce the dn/dT by 50% can be calculatedbased on volume using Equation 2, below.

v ₅₀=0.5(γ_(p)/γ_(p)−γ_(n))   Equation (2)

[0061] Wherein, v₅₀ is the volume % of the nanoparticles needed toreduce the dn/dT of the nanocomposite by 50% compared to the hostplastic; γ_(p) is the dn/dT of the host plastic (See FIG. 1); γ_(n) isthe dn/dT of the nanoparticle material.

[0062] For the combination of cyclic olefin homopolymer and magnesiumoxide, the volume (%) of nanoparticles needed to reduce the dn/dT of thenanocomposite by 50% compared to the dn/dT of the cyclic olefinhomopolymer is approximately 43%.

[0063] The invention has therefore been described with reference to apreferred embodiment thereof. However, it will be appreciated thatvariations and modifications can be effected by a person of ordinaryskill in the art without departing from the scope of the invention.PARTS LIST: 1 prior art lens 3 incident light 5 focal point of the lens7 range of change of the focal length produced by a change intemperature of the plastic lens 10 nanocomposite lens 12 reduced rangeof change of the focal length produced by a change in temperature of thenanocomposite lens 14 dispersed nanoparticles 15 representation ofnanoparticles dispersed into the host plastic material 16 plastic hostmaterial 20 schematic of method for making reduced dn/dT article 22 stepof selecting host material 24 step of selecting the nanoparticulatematerial 26 step of dispersion 28 step of forming an optical article 32compounding process 34 step of selecting host material 36 step ofselecting nanoparticulate material 38 step of surface treatingnanoparticles 40 step of compounding nanoparticles 42 step of formingthe nanocomposite into a useable form such as pelletizing 44solvent-based dispersion process 46 step of selecting host material 48step of selecting nanoparticles 50 step of dissolving host material insolvent 52 step of surface treating nanoparticles 54 step of dispersingnanoparticles in solvent 56 step of mixing together products of steps 50and 54 58 step of removing the solvent 60 step of foiming a useablearticle

What is claimed is:
 1. Polysulfone nanocomposite optical plastic, article comprises: a polysulfone host material having a temperature sensitive optical vector x₁ and nanoparticles dispersed in said polysulfone host material having a temperature sensitive optical vector x₂, wherein said temperature sensitive optical vector x₁ is directionally opposed to said temperature sensitive optical vector x₂.
 2. The polysulfone nanocomposite optical plastic article recited in claim 1 wherein each of said temperature sensitive optical vectors x₁ and x₂ are defined by a change in refractive index (dn) of said polysulfone host material and said nanoparticles, respectively, with respect to a change in temperature (dT).
 3. The polysulfone nanocomposite optical plastic article recited in claim 1 wherein said temperature sensitive optical vector x₁ has a negative value of about 100×10⁻⁶/degree C. and said temperature sensitive optical vector X₂ has a positive value in the range of about 6×⁻⁶/degree C. to about 50×10⁻⁶/degree C.
 4. The polysulfone nanocomposite optical plastic article recited in claim 1 wherein said nanoparticles are magnesium oxide.
 5. The polysulfone nanocomposite optical plastic article recited in claim 1 wherein said nanoparticles are aluminum oxide.
 6. The polysulfone nanocomposite optical plastic article recited in claim 3 wherein said nanoparticles are calcium carbonate.
 7. The polysulfone nanocomposite optical plastic article recited in claim 4 wherein said polysulfone host material comprises a predetermined volume (%) of said magnesium oxide nanoparticles to reduce said temperature sensitive optical vector x₁ by about 50%, said predetermined volume being determined by the equation: v ₅₀=0.5(γ_(p)/γ_(p)−γ_(n)); wherein v₅₀ is the volume % of said magnesium oxide nanoparticles needed to reduce the dn/dT of said polysulfone nanocomposite optical plastic article by 50% compared to said polysulfone host material; γ_(p) is the dn/dT of said polysulfone host material; and γ_(n) is the dn/dT of said magnesium oxide nanoparticles.
 8. The polysulfone nanocomposite optical plastic article recited in claim 7 wherein said predetermined volume (%) of said magnesium oxide nanoparticles dispersed in said polysulfone host material is about 42%.
 9. A method of manufacturing a polysulfone nanocomposite optical plastic article, comprising the steps of: (a) providing a polysulfone host material having a temperature sensitive optical vector x₁ and nanoparticles having a temperature sensitive optical vector x_(2,), wherein said temperature sensitive optical vector x₁ is directionally opposed to said temperature sensitive optical vector x₂; (b) dispersing said nanoparticles into said polysulfone host material forming a polysulfone nanocomposite material; and, (c) forming said polysulfone nanocomposite material into said polysulfone nanocomposite optical plastic article. 